2,6,10,10-Tetramethyl-1-oxa[4.5]deca-3,6-diene, having the formula ##STR5## was described in the art several years ago, for example in Swiss Patent No. 544,733. Whereas the above compound does not present any intereset for the man in the art, at least with respect to its organoleptic properties, we have now found surprisingly that the isomeric derivatives of formula I possess interesting organoleptic properties and, consequently, they can be advantageously used as odour- and flavour-modifying ingredients.